The so-called black-eyed pea or cowpea is not really a pea, but an African relative of the mung bean that was known to Greece and Rome and brought to the southern United States with the slave trade. It has an eye-like anthocyanin pigmentation around the hilum, and a distinctive aroma. A variety that produces a very long pod and small seeds is the yard-long bean, a common green vegetable in China.
From the book On Food and Cooking (2nd edition) by Harold McGee. © 2004 Harold McGee. By permission of Scribner, a division of Simon & Schuster, Inc.